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[ Instrument R & D of Instrument Network ] Lidar is a radar system that emits laser beams to detect the target position, velocity and other characteristic quantities. In terms of working principle, there is no fundamental difference with microwave radar: the detection signal (laser beam) is transmitted to the target, and then the received signal reflected from the target (target echo) is compared with the transmitted signal and processed appropriately , You can get the relevant information of the target, such as target distance, azimuth, altitude, speed, attitude, and even shape and other parameters, so as to detect, track and identify targets such as aircraft and missiles.
According to data from related agencies, the global lidar market will reach US $ 844 million in 2019, but will increase to US $ 2.273 billion in 2024, with a compound annual growth rate of 18.5%.
At present, the research team of Professor Tobias Kippenberg of the Federal Institute of Technology in Lausanne (EPFL) has found a new method for parallel measurement of frequency modulated continuous wave (FMCW) lidar using integrated nonlinear photonic circuits. This method couples a single-frequency continuous laser into a silicon nitride planar microcavity. Under the combined effects of dispersion, nonlinearity, cavity pumping and loss, the continuous laser is converted into a stable sequence of light pulses. The research results have been published in the journal Nature.
The first author of the study, Johann Riemensberger (postdoctoral fellow), said “surprisingly, the dissipative Kerr solitons not only persist when the pump laser is chirped, but also pass the chirp to it without distortion. All light combs produced. "
The small size of the microcavity results in a frequency spacing of 100 gigahertz between the generated optical combs, which is sufficient to separate them using standard diffractive optics. Since each comb tooth inherits the linear chirp characteristics of the pump laser, it is possible to create up to 30 independent frequency-modulated continuous wave (FMCW) lidar channels in the microcavity.
Each channel can simultaneously measure the distance and moving speed of the target, and the spectral separation of different channels makes the device no crosstalk between the channels. At the same time, the device can be integrated with an optical phased array based on a photonic integrated grating emitter.
The device emits light beams that can be spatially separated and operates in the 1550 nanometer optical band, which can relax the safety restrictions imposed by the human eye and camera. Anton Lukashchuk, a PhD student in the research team, said: "In the near future, the technology developed by the Federal Institute of Technology in Lausanne (EPFL) can increase the sampling rate of coherent frequency modulated continuous wave (FMCW) lidar by a factor of 10."
The principle of Frequency Modulated Continuous Wave (FMCW) lidar is different, it uses the principle of coherent laser ranging. Frequency modulation is performed on the laser to produce linear frequency chirp, and then the target distance is converted to radio frequency based on the hybrid heterodyne method.
The technical concept relies on high-quality silicon nitride microcavities, which are produced by the Micro-Nano Technology Center (CMi) of the Federal Institute of Technology in Lausanne (EPFL) and have ultra-low loss characteristics. Ligentec SA, a company incubated by the Federal Institute of Technology in Lausanne (EPFL), specializes in the manufacture of silicon nitride-based photonic integrated circuits (PIC), and can now order silicon nitride microcavities through the company.
This research work paved the way for the widespread application of coherent lidar in autonomous vehicles in the future. Researchers are now working to integrate lasers, low-loss nonlinear microcavities and photodetectors on-chip.